Steel sheet piles are long structural sections provided with an interlocking system that allows building continuous retaining walls. The most common sheet pile sections are: Z-sections, U-sections, Ω-sections, flat-web sections and H or double-T sections.
Z-section sheet piles include a first flange, a second flange, which is substantially parallel to the first flange, an inclined web, a first corner joining the web to the first flange, a second corner joining the web to the second flange, wherein each of the corners has an opening angle α greater than 90°, preferably in the range of 110° to 140°. The longitudinal edges of the flanges are generally equipped with coupling means for interlocking purposes. In distinct contrast to other sheet pile sections, Z-section sheet piles do not have a plane of symmetry.
It is well known in the art to produce Z-section sheet piles by a hot rolling process, starting from slabs or, more recently, from beam blanks. Different methods for hot rolling Z-section sheet piles are e.g. disclosed in following documents: U.S. Pat. No. 4,291,564, EP 0284827 A2, EP 0890395 A1, DE 2529405 A, JP 4/288903 A and U.S. Pat. No. 5,671,630.
U.S. Pat. No. 5,671,630 discloses a method for rolling such Z-section sheet piles from a beam blank. According to this method, a preform of the sheet pile is rolled with curved preforms of the web and the flanges. The curved preform of the web comprises: two web/flange transition sections, which are substantially flat sections parallel to the rolling plane; a middle section, which is a substantially flat section defining an angle of about 60° with the rolling plane; and two connecting bows, connecting the web/flange transition sections to the oblique middle section. The substantially “J”-shaped preforms of the flanges allow rolling the coupling means close to the neutral rolling plane. In a last rolling step, the curved preforms of the web and the flanges are straightened to form the finished Z-section sheet pile.
It is well known in the art that grooved rolls used for rolling Z-section sheet-piles have a relatively short lifetime. Due to the absence of mirror symmetry in their section, one has to produce one side of the Z-section sheet pile in a deep groove of the upper roll and the other side in a deep groove of the lower roll. Such extreme roll gap contours result in that the roll surfaces are rapidly worn out and in that possibilities for their reworking are rather limited. They also increase the risk of a roll fracture.
There is consequently a need for a method for rolling a Z-section sheet pile in which the rolls have a longer lifetime and are less exposed to a roll fracture.